Streamwise Extent and Ramp Rate Effects on Laminar Boundary Layer Response to Plasma Actuator Vortex Generators

Abstract

The unsteady output of a spanwise array of plasma actuators, arranged to generate streaks of high and low streamwise velocity in a Blasius boundary layer, is modeled numerically. When the forcing by the actuators undergoes a step change from off to on, the flow response downstream of the actuators is initially inverted in terms of the streamwise vorticity, disturbance velocity, and wall shear stress before approaching the steady-state behavior. The present study considers the effect of the length of the actuator in the streamwise direction and the effect of the rate change of the output of the actuator with respect to the nonminimum phase behavior. For the different rates of a gradually applied force, the body force increases linearly from zero to the same maximum value of the step, which simulates a reduced slew rate or ramped output. It is shown that the inverse flow response remains for the gradually applied input; however, the peak magnitude is less, and the overall response appears more damped. As the actuator length is reduced, while forcing was compensated for the shorter convective time over the actuator, the peak inverse response was enhanced.